Metal vapor laser tube

ABSTRACT

A metal vapor laser tube is comprised of an enclosure preferably in an elongate tubular form containing an amount of a metallic element. The material of the enclosure is selected to be electrically non-conductive and also for its ability to withstand elevated temperatures. The enclosure also has at least one window capable of transmitting energy at the wavelength of emission of the metallic element contained within the enclosure. Two electrodes, preferably in the form of cylinders, are oppositely disposed within the enclosure and an electrical conductor is connected to each electrode for external connection to a source of electrical energy. An extension of the enclosure is provided proximate to each electrode for containing the respective electrical conductors within a hollow capillary portion of the extension and also including an end portion of the extension which is sealed around the terminal of the electrical conductor to render it pressure-tight. The tube may be fabricated of quartz and the end portions of the extensions may comprise glass sealed to the quartz of the extensions which include the hollow capillary portion and also sealed around the terminal of each respective electrical conductor.

United States Patent [1 1 Richards Dec. 4, 1973 METAL VAPOR LASER TUBE[75] Inventor: William E. Richards, El Cajon,

Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

22 Filed: Feb. 3, 1972 21 Appl. No.: 223,201

[52] U.S. Cl 331/945, 313/219, 313/220, 313/227, 313/331 [51] Int. ClI-l0ls 3/02, l-lOls 3/22, l-lOlj 61/26 [58] Field of Search 313/220,227, 219, 313/331; 331/945 [5 6] References Cited UNITED STATES PATENTS2,162,505 6/1939 James et al. 313/220 OTHER PUBLICATIONS Kohl, Materials& Techniques for Electron Tubes, GT & B Tech. Series, Reinhold Pub. Co.,1960, pp. 18-23, & 394-396.

Primary Examiner-Ronald L. Wibert Assistant ExaminerR. J. WebsterAttorney-R. S. Sciascia et al.

[5 7] ABSTRACT A metal vapor laser tube is comprised of an enclosurepreferably in an elongate tubular form containing an amount of ametallic element. The material of the enclosure is selected to beelectrically non-conductive and also for its ability to withstandelevated temperatures. The enclosure also has at least one windowcapable of transmitting energy at the wavelength of emission of i themetallic element contained within the enclosure. Two electrodes,preferably in the form of cylinders, are oppositely disposed within theenclosure and an electrical conductor is connected to each electrode forexternal connection to a source of electrical energy. An extension of nthe enclosure is provided proximate to each electrode for containing therespective electrical conductors within a hollow capillary portion ofthe extension and also including an end portion of the extension whichis sealed around the terminal of theelectrical conductor to render itpressure-tight. The tube may be fabricated of quartz and the endportions of the extensions may comprise glass sealed to the quartz ofthe extensions which include the hollow capillary portion and alsosealed around the terminal of each respective electrical conductor.

6 Claims, 2 Drawing Figures METAL VAPOR LASER TUBE BACKGROUND OF THEINVENTION Certain metallic vapor laser tubes preferably are maintainedat elevated temperatures of the order of 900C-l000C for certain types ofdesired operation. Customarily, such laser tubes are enclosed within anoven to maintain the elevated temperature which causes the metallicelement contained within the sealed enclosure of the laser tube tovaporize. Electrically conductive electrodes sealed within the'lasertubes generate an arc therebetween from the application of a suitablesource of electrical energy to the external terminals leading from theelectrodes within the tube. The tube thus energized and maintained at asuitable temperature developing sufficient vapor pressure of themetallic element causes the metal vapor to be raised to an energy levelat which it will produce laser energy output. v

In the prior art, metal vapor laser tubes customarily included hotzones, generally disposed between the electrodes which generated theelectrical discharge. Moreover, the windows conventionally disposed ateither end of the laser tube for transmitting'the laser energy, weremaintained at a significantly lower temperature; the relatively lowertemperature is generally referred to as the cold zone. Though thewindows may not actually be operated at a truly cold temperature,

they were nonetheless cold relative to the hot zone.'As

a result, the operation of many prior art metallic vapor laser tubes waslimited in life and'efficiency because of the fact that the metalvapor'would migrate to the cold zone on the windows and'become depositedupon the windows by a partial condensation, thereby rendering thewindows partially opaque to the laser energy emitted, so that the laserbeam could not be efficien'tly transmitted outside the confines of thelaser tube.

Additionally, the hot metal in its vaporous form migrated ina continuousparticle flow to'the cold zone, and eventually there was very littlemetal remaining in the hot zone where the stimulated emission lasertakes place; as a result, the laser action after some determinativeperiod oftime just ceased to occur for lack of sufficient metal in thehot zone to develop sufficient vapor pressure to support and maintainlasing action.

In the prior art, in order to combat this problem many metallic vaporlaser tubes introduced an inert buffer gas such as argon, for instance,or helium between the hot zone and the relatively cold zones so that thewindows, for example, would be hopefully isolated from the metallicvapor and prevent the condensation of the metallic vapor upon thewindows the resultant undesirable diminished efficiency of operation.Al-

though the use of a buffer gas in prior art metallic vapor entdisadvantages which the presence of the buffer gas when there is anenergy transfer between the two gas systems which is not essential forpumping energy into the metallic vapor, it is possible that suchinteraction with the buffer gas can inhibit the desiredstimulatedemission.

Moreover, even with the advantages which the use of the buffer gasprovides in diminishing condensation of the metallic vapor on the coldwindows, eventually all the metal may be transposed from the hot zone tothe cold zone on thefwalls of the laser tube, for example, outside thehot zone. Consequently, after some determinable period ofoperation, thelaser tube must be replenished with an additional amount of metal toprovide the metallic vapor for the desired stimulated emission in thehot zone.

SUMMARY OF THE INVENTION The present invention contemplates that theentire laser tube containing the metallic vapor be maintained in anelevated temperature. This may be accomplished by an appropriatelyconfigured oven, for example, to change a metallic element to its vaporstate, developing an appropriate vapor pressure. Electrodes forimpressing the laser excitation, in the form of an electrical potential,across the metallic vapor are connected through electrical conductorswhich pass through hollow capillary passages in extensions of the mainenclo- I sure of the laser tube. These extensions may be of quartz, forinstance, where the main enclosure of the laser tube is also quartz,portions of the extensions adjacent the main enclosure being maintainedat approximatelythe elevated'temperatures of the main enclosure of'thelaser tube. The quartz extensions may preferably be fused to glass at apoint more remote from the heat of the main enclosure where they arerelativey cold. The glass end portions of the extensions are vacuumsealed to the electrical conductors which extend through the capillariesand connect with the electrodes for its energization by an appropriatesource of electrical'energy.

It has been found in the operation of the present invention that,because the entire laser tube assembly, apart from. end portions of itsquartz extensions, is maintained at the elevated temperature, themetallic vapor does not condense out on the windows which are usuallydisposed at opposite ends of a tubularly configured main enclosure ofthe laser tube; thus, there is no impairment of the transmission of thelaser energy emission out of the laser tube, as was the case in manyprior art'm'etallic vapor laser tubes employing cold windows.

Moreover, the concept of the present invention provides a gradual changefrom the hot zone to the cold zone through the use of the extensionsfrom the main enclosure, which extensions include a hollow capillaryportion wherein the conductors connected to the electrodes within thetube are received and passed through into a vacuum-sealed portion of theextension to an external terminal for connection to a source ofappropriate electrical energy.

In accordance with the concept of the present invention, it has beenfound that the metallic vapor does not migrate significantly from thehotzone because of the extremely small capillary dimensions within theextensions so that onlyan extremely small amount of metallicvaporcondenses out, if any; if a minute amount of metallic vaporcondenses-out within the hollow capillary portions of the extension ithas been found such condensed metal advantageously forms a seal aroundthe electrical conductor contained within the hollow capillary whichforms an operatively determined boundary between the hot and the coldzones.

Further, if quartz material is employed for the fabrication of themetallic vapor laser tube of the present invention, the main tubularportion and the windows,

as well as those portions of the extensions including the hollowcapillaries, may be made entirely of quartz to withstand the elevatedtemperatures necessary to achieve a desired stimulated laser emission.

Additionally, because of the fact that no significant amount ofcondensation will take place in the metallic vapor laser tube of thepresent invention, it is not necessary to frequently replenish theamount of metal within the tube. The highly desirable result is that themetallic vapor laser tube embodying the present invention has asignificantly longer operative life than metallic vapor laser tubes ofthe prior art.

In an embodiment of the present invention fabricated of quartz asdescribed hereinbefore, it has been found that a pressure-tight sealedunit can readily be achieved by fusing end portions of glass to thehollow capillary portions of the extensions from the tube;glass-tometals seals are thus facilitated around and about theconductors extending through the glass for connection to an externalsource of electrical energy.

Accordingly, the primary object of the present invention is to provide ametallic vapor laser tube which, in its operation, does not incurdisadvantages of prior art metallic vapor laser tubes.

Another primary object of the present invention is to provide a metallicvapor laser tube which is capable of operating with hot windows toobviate disadvantages of prior art metallic vapor laser tubes.

Another most important object of the present invention is to providesuch a metallic vapor laser tube which does not require the employmentof a buffer gas.

A further most important object of the present invention is to providesuch a metallic vapor laser tube which minimizes the migration of themetallic vapor thus extending the operative useful life of the tube.

These and other features, objects, and advantages of the presentinvention will be better appreciated from an understanding of theoperative principles of a preferred embodiment as described hereinafterand as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an isometric view of a metallic vapor laser tube embodying thepresent invention; and

FIG. 2 is an enlarged view ofa portion of the metallic vapor laser tubeillustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is an isometric view of ametallic vapor laser tube embodying the present invention. An enclosure10, which may take the elongate tubular form of the embodiment of FIG.1, contains an amount of a metallic element such as lead, for example,or any other suitable element capable of being raised to an energy levelto produce laser emission. The enclosure is selected for its ability towithstand elevated temperatures of the order of as much as 900 to1,000C, such as high grade quartz.

The metallic vapor laser tube as conceived by the present invention alsoincludes at least one window, such as the windows 11 and 12 illustrated,which are sealed to the ends of the enclosure 10. The windows 11 and 12are of material selected for its capability of transmitting energy ofthe wavelengths of emission of the metallic element chosen for themetallic vapor laser tube and included within the enclosure 10 asexplained hereinbefore. In the embodiment illustrated in FIG. 1, thewindows 11 and 12 are preferably required to be optically flat forgreatest efficiency of operation in transmitting laser energy.

Two electrodes 13 and 14 are disposed within the enclosure 10 at itsopposite ends. The electrodes 13 and 14, of the embodiment illustratedin FIG. 1, are in cylindrical form so that the laser energy which isgenerated in the enclosure 10 may pass axially through their respectivehollow interior axes and out the respective windows 11 and 12. Theelectrodes 13 and 14 each have an electrical conductor 15 and 16,respectively, arranged and connected for external connection to asuitable source of electrical energy. The electrical conductors 15 and16 pass through respective extensions 17 and 18 from the enclosure 10proximate to the respective electrodes 13 and 14.

Each extension, such as that shown at 17 on the lefthand side of FIG. 1,has a hollow capillary portion 19 and 20 adjacent the enclosure 10. Therespective associated electrical conductors 15 and 16 pass through thehollow capillary portion 19 and 20 of the extensions 17 and 18.

The portion of the extensions 17 and 18 adjacent the enclosure 10 whichinclude respective hollow capillary portions 19 and 20 may be fabricatedof quartz of substantially the same grade and high quality as the quartzmaterial which is suitable for the fabrication of the enclosure 10. Inthe preferred embodiment of the present invention the end portions 21and 22 of the extensions 17 and 18, respectively are sealed around therespective terminal portions 23 and 24 of the electrical conductors 15and 16 to provide a vacuum tight assembly.

A suitable high grade glass is readily adaptable to provide the endportions 21 and 22 of the extensions 17 and 18, respectively, and may besealed to the adjacent quartz portion of each respective extension asillustrated in FIG. 1. Additionally, the glass end portions 21 and 22may readily be fabricated to provide an excellent glass-to-metal sealwith the terminal portions 23 and 24 of the conductors l5 and 16.

FIG. 2 is an enlarged portion of one end of a preferred embodiment ofthe present invention as illustrated in FIG. 1. Like elements asillustrated in FIG. 2 bear the same numerical designation as FIG. 1.

As previously explained, one of the primary difficulties anddisadvantages of prior art metallic vapor laser tubes was that thevaporized metal tended to migrate from the hot portion of the tube,which may typically be operated at the temperature of the order of 900Cor more, to the cold portions of the tube so that some of the metallicvapor would condense out on the colder portions of the assembly. Thisaction resulted in two principal disadvantages: one disadvantage is thatthe condensation of metal vapor on a cold window diminishes theefficiency of transmission of the laser energy to the outside of thetube. The present invention has overcome that problem by providing thatthe entire assembly, including the enclosure 10 and the windows 11 and12, is operated at an elevated temperature so. that there is a greatlydiminished tendency of the metallic vapor to migrate to the windows 11and 12 and form a condensing film of their own. I

The other principal disadvantage of prior art laser tubes was that themetallic vapor would tend to migrate to other cold portions of theassembly, condensing out on the cold portions so that eventually verylittle of the selected metallic element in vapor form would remain toperform its lasing function. This disadvantage has been obviated in theprsent invention by providing that there be an appropriate gradualchangefrom the hot portion of the metallic vapor laser tube, asrepresented by the enclosure with its windows 11 and 12, to the coldportion, as represented by the terminals 23 and 24 of the electrodes 15and 16. This is accomplished by providing that extensions, such as17-and 18 illustrated in FIG. 2 proximate to each one of the electrodes13 and 14, be fabricated to have hollow capillaries as illustrated at 19and 20 in FIG. 2, through which the hot electrical conductor 15 passes.

Each of the extensions and the electrical conductor contained within it,gradually cools from its hottest point where it is connected to theelectrode 13, for example, as shown in FIG. 2, to its external terminal23 which connects to an appropriate source of electrical energy. Thehollow capillary portion of 19, for example, of the extension of 17 issufficiently small as to prevent significant migration of the metallic,vapor along its path. Moreover, the electrical conductor connected toeach electrode 13 and 14 as illustrated by the electrical conductor 15of FIG. 2 gradually becomes cooler as it passes through the hollowcapillary l9 and is relatively cold at the point it is enclosed in thesealed end portion 21 of the extension 17.

Moreover, it has been found that even if some very small quantity of themetallic vapor does migrate down and along the hollow capillaryportions, such as illustrated in 19 in FIG. 2 of the extension 17,thatminute amount of metallic vapor, upon condensation, (if it doescondense and cool) will effectively seal off the hot portion of theextension 17 from its cold portion, thus actually contributing to andaiding the transition from the hot operative portion of the assemblyfrom the cold portion of the assembly without significantly diminishingthe amount or the vapor pressure of the vaporized metallic elementcontained within the enclosure 10.

Operation In the practice of the present invention the metallic vaporlaser tube is fabricated preferably in a configuration as illustrated inFIG. 1 and 2 and of suitable materials as previously described. With theend portions 21 and 22 of the two extensions 17 and 18 sealed to therespective electrical conductors 15 and 16 to form vacuum-tight selas,the enclosure 10 is then evacuated through an opening such as that shownat 25. The metallic element is then introduced into the interior ofenclosure 10 by distillation, the metal coating the inner walls ofenclosure 10. Thereafter the opening is sealed off.

In operation the entire laser tube is placed within a suitable heatingmeans, such as an oven capable of maintaining the desired temperature,and an appropriate source of electrical energy is applied to theterminals 23 and 24 of the electrical conductors 19 and 20. Upon theapplication of a suitable source of electrical energy, the dischargeoccurs between the two electrodes 13 and 14, raising the vaporizedmetallic element to an energized state which is sufficiently high tocause laser emission. The laser emission is transmitted through windows11 and 12 to be employed as desired.

An embodiment of the present invention will produce laser energy forrelatively long life because of the virtual elimination of migration ofthe metallic element from the area wherein it is vaporized and performsits lasing function. This is made possible by the concept of the presentinvention which provides for a hollow capillary leading through aportion of an extension from the main element enclosure 10 of the lasertube which is sufficiently large to contain an electrical conductor, butyet small enough so that no significant amount of migration of themetallic element will take place.

Furthermore, the concept of the present invention provides that theextensions from the main element of the laser tube enclosurewill be suchthat the portion of each of the extensions, including the hollowcapillary, will be hot where it joins the enclosure, but will be cold atits opposite extremity in the sense that significantly reducedtemperature is maintained in that region. The temperature graduallybecomes lower along each extension, diminishing from the elevatedtemperature of the hot portion attached to the enclosure, to the coldportion which provides the external terminal connection for theelectrical conductors.

Additionally, the concept of the present invention, particularly withrespect to the configuration and fabrication of the extensions from theenclosure makes possible a reliable, vacuum tight seal, preferably madeto a high grade glass which is fused to the ends of the quartz portionof each extension, which seals will best withstand the rigors ofoperation of the metallic vapor laser tube.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A metal vapor laser tube comprising:

an enclosure containing an amount of a metallic element,

said enclosure being of an electrically nonconductive material selectedfor its ability to withstand elevated temperatures and having at leastone window capable of transmitting energy at the wavelength of laseremission of said metallic element, I

two electrodes oppositely disposed within said enclosure;

an electrical conductor connected to each electrode for externalconnection to a source of electrical enan extension from said enclosureproximate to each electrode;

a hollow capillary portion in each said extension adjacent saidenclosure for receiving said electrical conductor in spaced dispositionfrom the inner capillary walls,

each said hollow capillary portion being dimensioned to preventsignificant migration-of metallic vapor therein; and,

an end portion'of each said extension sealed around the terminal of saidelectrical conductor.

axially aligned with the central axis of the tubular configuration ofsaid enclosure.

'6. A metal vapor laser tube as claimed in claim 1 wherein saidextensions containing said hollow capillary portions are quartz and saidend portions are glass sealed to said quartz and around the terminals ofsaid electrical conductors.

IF OK i l

1. A metal vapor laser tube comprising: an enclosure containing anamount of a metallic element, said enclosure being of an electricallynon-conductive material selected for its ability to withstand elevatedtemperatures and having at least one window capable of transmittingenergy at the wavelength of laser emission of said metallic element, twoelectrodes oppositely disposed within said enclosure; an electricalconductor connected to each electrode for external connection to asource of electrical energy; an extension from said enclosure proximateto each electrode; a hollow capillary portion in each said extensionadjacent said enclosure for receiving said electrical conductor inspaced disposition from the inner capillary walls, each said hollowcapillary portion being dimensioned to prevent significant migration ofmetallic vapor therein; and, an end portion of each said extensionsealed around the terminal of said electrical conductor.
 2. A metalvapor laser tube as claimed in claim 1 wherein said enclosure isfabricated of quartz.
 3. A metal vapor laser tube as claimed in claim 1wherein said enclosure is tubular in shape.
 4. A metal vapor laser tubeas claimed in claim 3 and including an optically flat window sealed toeach end of said enclosure.
 5. A metal vapor laser tube as claimed inclaim 4 wherein said electrodes are cylindrically shaped and axiallyaligned with the central axis of the tubular configuration of saidenclosure.
 6. A metal vapor laser tube as claimed in claim 1 whereinsaid extensions containing said hollow capillary portions are quartz andsaid end portions are glass sealed to said quartz and around theterminals of said electrical conductors.